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Additional recommended knowledge
A two stage approach proved to be the key to successful synthesis of pure digallane. Firstly the dimeric monochlorogallane, (H2GaCl)2 (containing bridging chlorine atoms this can be formulated as (H2Ga(μ-Cl))2) was prepared via the hydrogenation of gallium trichloride, GaCl3 with Me3SiH. This was followed by a further reduction with LiGaH4, solvent free, at −23°C to produce digallane, Ga2H6, in low yield.
Digallane is volatile and condenses at −50°C to give a white solid.
Structure and bonding
Electron diffraction measurements of the vapour at 255°K show the structure of digallane to be similar to that of diborane with 2 bridging hydrogen atoms. The terminal Ga-H bond length is 152pm, the Ga-H bridging is 171 pm and the Ga-H-Ga angle is 98°. The Ga-Ga distance is 258pm. The NMR spectrum of a digallane solution in toluene shows to peaks attributable to terminal and bridging hydrogen atoms.
Digallane decomposes at ambient temperatures:
The reactions with Lewis bases are similar to those of diborane. With trimethylamine 1:1 and 2:1 adducts are formed i.e. NMe3.GaH3 (NMe3)2.GaH3. With phosphine a 1:1 adduct PH3.GaH3. The trimethylamine adducts have been known for some time.   They were prepared by the reaction of LiGaH4 with trimethylammonium chloride, Me3NHCl, the 2:1 adduct is formed at low temperatures:
The structure of Me3N.GaH3 was reexamined and it has been confirmed to be monomeric in both the gas and solid phases. In this it contrasts with the corresponding alane adduct, NMe3.AlH3 which in the solid is dimeric with bridging hydrogen atoms.  A range of other 1:1 adducts have been prepared and their stabilities determined. 
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Digallane". A list of authors is available in Wikipedia.|